Fix wrong init dependency on markup extensions (#7038)

* fix wrong init dependency on markup extensions

modules/markup/markup.go

@@ -15,6 +15,14 @@ import (
 func Init() {
 	getIssueFullPattern()
 	NewSanitizer()
+
+	// since setting maybe changed extensions, this will reload all parser extensions mapping
+	extParsers = make(map[string]Parser)
+	for _, parser := range parsers {
+		for _, ext := range parser.Extensions() {
+			extParsers[strings.ToLower(ext)] = parser
+		}
+	}
 }
 
 // Parser defines an interface for parsering markup file to HTML